In recent years, a greater environmentalist awareness has been generated, from which surged a tendency for the development of investigation directed toward taking care of the environment, mainly for obtaining clean fuel from petroleum refining. Obtaining gasoline and diesel with deep desulfurization is becoming more difficult in view that the crude petroleum contains high contents of sulfur, nitrogen, oxygen, other pollutants, and higher density. On the other hand, environmental regulation tends toward lower levels of sulfur each time. This factor has been, in recent years, the main motor for the great increase in the implementation of catalysts development. The challenges faced by catalyst suppliers are mainly increased, catalytic activity in hydrotreatments (HT) required addressing the specific demands of fuel markets with ultra-low sulfur content (<10 PPM before 2010).
In order to reach the regulated established levels, especially for the sulfur content, it is necessary to have catalytic materials able to be active even with the most refractory molecules present in the different raw materials. To do this, several attempts had been carried out for developing new and more active catalysts with appropriate functionality to produce HDS in these molecules. The strategies include: the use of new active phases such as carbides, nitrides, phosphides, or different transition metal sulfides of Mo and W, promoted with Ni or Co. The operation of these phases continues to be explored for practical uses. The development of various sophisticated synthesis methods, require extreme pressure and temperature conditions and the generation of very complex systems that include tri-metallic catalysts.
Transitional metal sulfides (SMT) have been the more highly used systems due to their exceptional resistance to poisoning, as well as their catalytic characteristic on hydro processing reactions, mainly the catalysts formed by MoS2 or WS2, which should be stable to hydrodesulfurization (HDS) conditions, commonly at temperatures between 300-400° C. and pressure of H2 of 490 psi.
The SMT, which can be supported or unsupported, have been prepared by diverse and very various synthesis methods among emphasize comaceration and homogeneous precipitation. However, the obtained materials, which are generally oxides, hardly reach a complete sulfidation, so the thiosalts precursor decomposition is a very interesting alternative preparation method, which may provide an easy way to achieve a high level of sulfidation in SMT final catalyst. This method may be applied to the development of both material types, meaning, unsupported and supported.
For obtaining supported materials are mainly used as (γ)-alumina, mixed oxides, carbon, zeolites, mesostructured material based silicon oxide, etc. On the other hand, unsupported catalysts or “massic” only contain the active phase of SMT, bi-metallic and more recently as tri-metallic. The second and third metal, commonly referred to as promoters, enhance the catalytic performance of the HT. The transition metal sulfides are commonly promoted with elements of Group VIII B (cobalt and/or nickel) due to the balance between performance and economy. Regardless of the synthesis method used for HDS catalysts preparation, these materials should have specific characteristics such as high catalytic activity, low crystalline degree, or weak crystalline structure, as well as good texture properties, such as high surface area and homogeneous pore size distribution.
Even though supported catalysts are more economically attractive materials for industrial use, in general they are less efficient than the unsupported, because an interaction exists between the metal and the support. This modifies the morphology of the active phase and affects the reducibility to be supplied by the sulfur, among other things. Therefore, there is great interest to develop unsupported catalysts through simple, economic methods with low environment impact.
Recently, G. Alonso, J. Yang, M. H. Siadati and R. R. Chianelli, lnorg Chim Acta, Vol 3 25, (2001), Pages 193-194, G. Alonso, G. Aguirre, I. A. Rivero, S. Fuentes, lnorg. Chim. Act 274 (1998), Page 108, G. Alonso, G. Berhault, lnorg. Chim. Acta 316 (2001), Page 105, L. Alvarez, J. Espino, C. Ornelas, J. L. Rico, M. T. Cortez, G. Berhault and G. Alonso, J. of Mol. Catal. A: Chemical, Vol 210, (2004), page 105-117, G. Alonso, V. Petranovskii, M. Del Valle, J. Cruz-Reyes, a. Licea-Claverie, S. Fuentes, Appl. Catly A: Gral (2000), 1997, Pags. (87-90), prepared unsupported HDS catalysts based on the thiometalatos tetraalkylamonium synthesis. This synthesis is based on the methodology developed by J. W. McDonald, G. D. Friesen, I. D. Rosehein, W. E. Newton, lnorg, Chem. ACTA 72 (1983), Page. 205, for the ammonium thyomolybdate synthesis (ATM) in aqueous solution, which subsequently is reacted with tetraalkylamonium salts to increase the catalyst surface area after its activation. Generally, the generated thiosalts are activated by using different routes such as: in situ activation, where the activation takes place simultaneously with the application or on extremely high hydrogen pressure conditions (up to 2000 psi); while activation ex situ, involves the previous decomposition of the precursors before the HDS reaction, which takes place at atmospheric pressure under a specific gas mixture flow (mainly H2S/H2) at typical temperatures of 300-500° C. These synthesis and activation methods, widely reported, have some important disadvantages: the synthesis departs from costly molecules such as the salts of tetraalkylammonium, while in activation, the via in situ requires extreme pressure conditions to achieve good catalytic activities, on the other hand the ex situ way, requires a mixture of gases which includes H2S known for its high toxicity and environmental impact.
Among the more active commercial unsupported catalysts in hydrodesulfurization are trimetallic materials composed by Ni—Mo—W (NEBULA and STAR catalyst developed by Exxon Mobil-Albemarle), in the case of NEBULA has been reported that presents a great activity (up to three times that of any other catalytic system, KNEBULA≈31.2×10−7 mol g−1 s−1, evaluated in a reactor by batch at 350° C. and 490 psi) and high HDS stability. Even if the technological contribution of these materials is obvious, it is important to highlight that its use significantly increases the production cost for clean fuels, so its use is limited to certain beds or layers of the catalyst bed, which mission is to treat flows having high content of nitrogen compounds, the following layers are filled with cheaper materials, generally supported, that allow an overall result that complies with regulations.
It is so obvious, the need for efficient and low-cost materials. In this light, Y. Gochi-Ponce, I. Alvarez-Contreras, f. Paraguay-Delgado and g. Alonso-Núñnez, Int. J. Materials and Product Technology, Vol. 27, Nos. 1/2 (2006), Pages 130-140, reported trimetallic catalysts Ni—Mo—W with 5, 25, and 50% by weight of AL2O3, using a multiple stage synthesis method with strict pH control, followed by calcination, and subsequent ex situ activation phase at 400° C. in the presence of a dimethyl-disulfide mixture (DMDS)/N2. This method is an alternative that prevents the use of high pressure for the generation of non-supported trimetallic catalysts. However, complex synthesis coupled with the use of DMDS, which may be fatal if inhaled, is highly toxic and irritating in contact with the skin and respiratory tract; creates a strong disadvantage.
In summary, environmental regulations continually diminish the permitted level of emissions, which requires the generation of more efficient HDS catalytic systems. Today the most widely used catalysts at the industrial level are based on SMT, generally supported in Al2O3. Its great use is based on its low cost. However, considering the effectiveness required for sulfur removal, the most suitable option is the use of non-supported catalysts, which to be efficient normally requires complicated synthesis methods and compositions with a high metal content, which increases its cost and reduces the feasibility use. In this framework, a simple, safe, economic and environmentally friendly method to allow having competent catalytic materials with those obtained today by more complex methods, offers unsuspected possibilities from the industrial application point of view. Thus, the present invention from the commercial point of view, presents advantages when considering the simplicity of the synthesis method, which will affect the catalyst cost, as well as the reduction of the environmental impact from the synthesis.
There are currently some patents describing methods for obtaining unsupported catalysts. In the description of such patents the high metal content of the catalytic is evident (with the consequent high cost) and the severe conditions required for the catalytic activation. The patents are as follows:
In the U.S. Pat. Nos. 6,299,760; 6,156,695; 6,783,663; 6,712,955 and 6,758,963 disclose preparation methods and the implementation of new unsupported catalysts NiMoW. It was found that new NiMoW catalysts exhibited a HDS activity three times higher than a commercial catalyst. The catalyst preparation method forms the NiMoW precursor using ammonia as a chelating agent, followed by calcination, and sulfuretion of the final NiMoW catalyst. The preparation method has several disadvantages such as the use of concentrated aqueous ammonia that causes environmental pollution and the synthesis method involves a high preparation cost of the catalysts.
U.S. Pat. No. 7,223,713 B2 describes a producing method for molybdenum disulfide catalysts (MoS2) and molybdenum disulfide with carbon, containing (MoS2-xCx) that show high values of surface area due to the hydrothermal processes involved in the synthesis. The catalysts are formed from precursor salts with the general formula AxMoS4, where A is an ammonium ion or tetraalkylammonium (x is 2 for each case). The obtained molybdenum disulfide can be used alone or with promoters such as cobalt, ruthenium, iron or nickel. The MoS2 can be obtained in aqueous solutions or a mixture of aqueous and organic compounds under hydrothermal conditions. The process is suitable for large scale implementations such as batch reactors at high pressures (100-2000 psi) to 300 or 400° C.
The U.S. Pat. No. 7,132,386 B2 describes a technique to improve the mass production of amorphous type sieve material which, among other things, are very useful as catalysts for a wide variety of applications such as a hydrotreatment process. The catalysts are obtained in aqueous solution of ammonium thiomolybdates and tetraalkylammonium salts activated under pressure from 20 up to 4950 psi. The disadvantage is the cost of reagents for the precursor's generation and activation under high pressure conditions that generally increase the cost of obtained material and limits their industrial exploitation.
Patent United States No. 7,687,430 B2 describes a preparation process for a solution consisting of at least one cobalt or nickel salt, in at least one heteropolyanion combined with molybdenum and cobalt or molybdenum and nickel in its structure, the preparation process includes: a) the mixture for at least one molybdenum source and at least one oxidizing compound in aqueous solution for synthesizing paramolybdate ions in acid pH, with a molar relation range of 0.1 to 20; b) introduction of at least one cobalt precursor and/or at least one nickel precursor in the solution a) with a molar ratio (Ni+Co)/Mo between 0.25 and 0.85.
The United States Patent Application Publication No. 2009/0145808 A1 describes a process catalyst synthesis for hydrodesulfurization by spray pyrolysis. The catalyst particles may include at least one metal selects between molybdenum, cobalt or nickel and a carbon dioxide support. The spray pyrolysis technique allows obtaining catalytic particles with high loading catalyst on the substrate. The support may be Aerosil 300, among others.
The United States Patent Application Publication No. 2010/0193402 A1 describes a catalyst composed of metal oxide, having a particle size of 10 nm to 100 nm and the reactive species have a structure containing multi-metallic oxides, consisting of one metal of the group VIII and two metals of the group VIB, wherein the molar ratio of the metal of Group VIII to the metal of group VIB metal is 1:9 to 9:1 preferably 1:6 to 6:1 and more preferably 1:4 to 4:1 and the molar relationship between the two metals of group VIB is 1:5 to 5:1, preferably 1:3 to 3:1, more preferably of 1:2 to 2:1. Another aspect that describes this application is a method for obtaining a catalyst with multiple phases which include the formation of an aqueous suspension of a carbonate of the metal group, formation of aqueous salts solution of metals of group VIB adding a surfactant. The disadvantage is that there is a relatively long method that involves the surfactants use and various thermal treatments.
The United States Patent Application Publication No. 2010/0210741 A1 describes a method for obtaining and a catalyst composition based on cobalt molybdenum sulfide, although the implementation of this catalyst is directed to the production of stable alcohol from synthesis gas.